JPS62209733A - Optical head for optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the number of parts, and heighten assembling accuracy, by using a half prism which is shaped in a cylinder type, and functions as an enlarging and correcting lens, and obtaining a focus servo error signal by light beams on a photodetector only in a uniaxial direction with a lens function. CONSTITUTION:The light beams from a semiconductor laser 1 is divided into plural diffracted light beams at a diffraction grating 2, however, te beams to concentrate light energy to 0th order and + or -1st order beams, are used. Those beams transmit a half prism 10, and are condensed on a disk 6 with an objective lens 5, then being reflected on the disk 6, and change directions at the prism 10, and arrives at a light detector 8. Out of those beams, the 0th order beams are made incident on photodetectors B1-B4, and the + or -1st order beams, on light receiving parts A1 and A2. At such a time, the prism 10 is formed in a cylindrical shape, and performs the lens function in a vertical uniaxial direc tion, and when a distance between the lens 5 and the disk 6 is dislocated, a spot on a light receiving plane becomes an ellipse, and the focus servo error signal can be obtained by taking a signal of (B1+B3)-(B2+B4).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head for an optical information recording/reproducing apparatus that records or reproduces information by focusing optical spoilers 1 to 1 on a disk.

[Prior art l] Figure 3 is a diagram showing the optical system of a conventional optical head. In the figure, (1) is a semiconductor laser as a light emitting source;
2) is a diffraction grating fixed to a holder (3), (4) is a half prism, (5) is an objective lens, (6) is a disk, (7) is a magnifying lens, (8) is a photodetector, (9) is a knob for adjusting the position of the diffraction grating (2) by inserting an eccentric shaft (9a) into the fourth part (3a) of the holder (3) and rotating it in the direction of the arrow.

Next, the operation will be explained. After the light emitted from the semiconductor laser (1) enters the diffraction grating (2), it is split into multiple diffracted lights, but the optical energy is concentrated in the 0th order ±1st order and these three light beams are used. .

The three light beams pass through the half prism (4), are focused onto the disk (6) by the objective lens (5), and after being reflected on the surface of the disk (6), the direction is changed by the half prism (4). and passes through a magnifying lens (7) to a photodetector (8).

As shown in Figure 4(a), the three diffracted lights are focused at an angle to the bit string on the disk (6), and among the reflected lights, the 0th order light is shown in Figure 4(b). As shown, the primary light is applied to the light receiving elements 81 to B4 of the photodetector (8), and the - primary light is incident on the light receiving section at 1°A2.

The zero-order light is used as a signal on the disk and as an error signal for focus servo. That is, by the magnifying lens (7),
Since the lens effect works only in the axial direction connecting the light-receiving elements B and -83 (or B2-84), if the distance Nt between the objective lens (5) and the disk (6) deviates, spora 1- is an ellipse, 11+83 ) −(82+l
By taking the signal of 34), the error signal of the focus servo can be obtained. In addition, the ±1st-order light is a difference signal (IA1-
IA2) is created and used as the error signal for the ]-rack servo.

[Problems that the invention attempts to solve] Conventional optical heads are configured like twins, so
There were problems such as the need to precisely align the magnifying lens on the optical axis, and the precision of the built-in base and the accuracy of the lens were required.

This invention has been made to solve the above-mentioned problems, and aims to reduce the number of parts in the assembly process and to provide an optical head that does not require assembly precision.

[Means for Solving the Problems] The optical head according to the present invention combines the action of a magnifying lens with a half prism! It was designed so that

[Function] The half prism in this invention has a cylindrical shape and has the function of a magnifying lens, so that the light to the light receiving element is 1
The focus servo error signal can be obtained by receiving the lens action only in the axial direction, and the reduction in the number of parts improves the sewing accuracy.

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, in which the same members as in FIG. 3 are given the same reference numerals,
(10) is a half prism formed into a cylindrical shape so as to function as a magnifying lens.

Next, the operation of the above embodiment will be explained. After the light emitted from the semi-reflective body 1 noser (1) enters the diffraction grating (2), it is split into multiple diffracted lights υ1.
Next, concentrate and use these three beams of light. This 3
The light beam from the book passes through the half prism (10), is focused onto the disk (6) by the objective lens (5), is reflected onto the surface of the disk (6), and then is directed by the half prism (10). and reaches the photodetector (8).

As shown in Figure 2(a), the three diffracted lights are separated by the disk (
6) Above, the light is focused at an angle to the pit row, and among the reflected light, the 0th order light enters the light receiving element of the photodetector (8), 81 to B4, as shown in FIG. 2(b). 1, ±1
The secondary light enters the light receiving sections A1 and A2.

The zero-order light is used as a signal on the disk and as an error signal for focus servo. In other words, since the half prism (10) has a cylindrical shape, when considering two vertical axes, the lens action works only in one axis direction, and the distance between the objective lens (5) and the disk (6) is shifted. In this case, the focus servo error signal can be obtained by taking the signal of 4T (B1 + B3) - (B2 + R4) when the spot on the light receiving surface is an ellipse. Moreover, the ±1st order light is detected by the light receiving section △1. A track servo error signal is generated by the signal A2.

[Effect of the invention 1 As described above, according to the present invention, since the shape of the half prism is made cylindrical, the half prism can function as a magnifying lens, reducing the number of parts and improving assembly accuracy. It has the effect of increasing the

[Brief explanation of drawings]

FIG. 1 is an optical system diagram of an optical head according to an embodiment of the present invention, FIGS. 2(a) and (b) are spot state diagrams on a disk and a light receiving element by the optical system, and FIG. 3 is a diagram of a conventional optical head. The optical system diagrams of the optical head, FIGS. 4(a) and 4(b), are state diagrams of spots on the disk and light receiving element due to the optical system. In the figure, (1) is a light emitting source (semiconductor laser), (6
) is a disk, and (10) is a half prism. In addition, in the figure, the same month indicates the same or equivalent part.

Claims (1)

[Claims] In an optical head installed in an optical information recording/reproducing device, which records or reproduces information by focusing a light spot on a disk, a half prism separates the light emitted from the light source and the light reflected from the disk. An optical head for an optical information recording and reproducing device, characterized in that the optical head also serves as a cylindrical lens that generates an error signal for a focus servo that reliably focuses a light spot on the disk.